The present invention relates to a method and apparatus for connecting electric wires mutually and conductively, the electric wires being arranged in parallel to each other in a wire harness or the like.
As a conventional method of connecting the end portions of electric wires to each other, there are available well-known methods that are disclosed in Japanese Patent Publication No. 4-33287 and Japanese Utility Model Publication No. 63-157163. In one of the well-known methods, as shown in FIG. 6, the insulating coatings 4 of electric wires 1 to be connected are removed to provide exposed conductors, and the exposed conductors are collected to provide a collective conductor 3. The end portions of the electric wires 1 including the collective conductor 3 are covered with an insulating tube 12. While the insulating coatings 4 of the electric wires 1 are inserted into and held by one of two openings formed in the two end portions of the insulating tube 12, the insulating coatings 4 are welded to the end portion of the insulating tube 12 to close the connecting portions.
In another conventional method, as shown in FIG. 7, the end portions of the electric wires 1 including the collective conductor 3, similarly formed by collecting the exposed conductors, are inserted between and held by two upper and lower insulating sheets 13, and the peripheral edges of the insulating sheets 13 are welded together.
In both of the conventional connecting methods, the connecting portions of the electric wires wrapped in the insulating tube 12 or sheet 13 are shut off from the open air to stop respiratory action of the electric wires. Respiratory action is an action in which the air is ventilated from one end of an electric wire to the other through gaps across the wire due to the expansion and contraction of the air caused by the varying temperatures of a connector of the end portion of the electric wire or the like. Wrapping of the wires in this manner prevents water from entering from the connected end portions of the electric wires.
In the above-mentioned well-known methods, however, because air is trapped within the insulating tube 12 or sheet 13 during the welding process, the air can be condensed into dew according to the temperatures of the connecting portion of the insulation tube or sheet, with the result that the connecting portion can rust and a slight respiratory action can be produced in the connected wires. In addition, because the insulating tube 12 and the sheet 13 include a plurality of peripheral edges to be welded, and there is a danger that the open air can be ventilated due to the poorly welded edges and high quality connected wires are hard to obtain. In addition, a plurality of points must be checked to prevent the poor welding, which results in complicated working management.
Further, in the above well-known connecting methods, because a plurality of peripheral edges of the insulating tube 12 or sheet 13 must be welded, a large-size welding mold is required and the weld working is complicated. Besides, in welding, it is difficult to position the collective conductor 3 with respect to the insulating tube 12 or the like, which requires much labor and time for welding and thus the costs of the connected wires are expensive. In addition, the insulating tube 12 or sheet 13 must be fairly larger in size than the collective conductor 3 to be wrapped therein and thus the insulating tube 12 or sheet 13 provides a dead zone. This inevitably causes the connecting end portion of the insulating tube with the collective conductor to become large in size. However, such large-size connecting end portion is contrary to the demands for reduction of the size of the wire harness system, which should be as compact as possible.